Exosome-mediated signaling in neuropathic pain Chronic neuropathic pain resulting from injury or malfunction of the nervous system is extremely difficult to treat. Unlike physiological or acute pain, where pain ceases after the damaged nerves or tissue heal, neuropathic pain can result in allodynia (pain from a non-painful stimulus) and hyperalgesia (heightened sensitivity to pain). The profound differences between acute and chronic pain indicate that pain results from the engagement of highly plastic molecules and circuits. Exosomes are 30-100 nm vesicles that carry mRNAs, miRNAs, proteins, and lipid mediators to recipient cells via circulation. Cells use these vesicles to communicate with both adjacent and distant cells. The molecules present on the surface of these vesicles enable them to target recipient cells. The exosomal contents vary depending on the source and the physiological conditions of cells releasing them, as well as on disease states that are known to alter exosome composition. However, not everything that is present in the parent cell is incorporated into the exosomes, suggesting that this well-regulated process is dynamically altered by signaling cues. Exosome uptake results in modulation of gene expression in recipient cells and represents a novel mechanism of cellular communication. There are no studies to date investigating alterations in exosome composition, function, and signaling mechanisms in a neuropathic pain state. Our preliminary data characterizing exosomes in serum from a mouse model of neuropathic pain four weeks after surgery showed a distinct exosomal miRNA and protein signature compared to sham control. We hypothesize that alterations in exosomal composition following nerve injury render them pronociceptive and contribute to the maintenance of chronic neuropathic pain. Using in vitro, ex vivo and in vivo approaches, we will investigate gene expression changes induced by uptake of exosomes from the serum of nerve injury model compared to sham control mice. Differences in exosomal uptake by recipient cells, preference for neurons, astrocytes or glia, alterations in proinflammatory mediators, thermal and mechanical hypersensitivity induced by exosomes and reversal of hypersensitivity by inhibition of exosome release will be investigated. These studies will provide insights on novel signaling mechanisms resulting from exosome release under chronic neuropathic pain and their role in the maintenance of pain. Elucidation of functional properties of exosomes can be beneficial in developing novel therapeutic intervention strategies to treat chronic pain.